Vehicle safety systems of the type incorporating passive passenger restraints, as safety devices, have been known for some time. Such systems generally comprise at least one inflatable confinement, such as an inflatable bag or inflatable seat belt, which is inflated to restrain movement of a vehicle occupant during a collision. In systems of this type, the confinement is inflated when a crash sensor switch detects a vehicle deceleration of a predetermined magnitude indicative that a collision is occurring. Closure of the crash sensor switch completes an electrical circuit for flowing current to energize an actuator for the vehicle safety device. The actuator is frequently an electro-explosive device, incorporating a detonator coil, which upon energization causes the confinement to be inflated to an expanded, passenger restraining condition. A system of the general type above discussed, and to which the present invention may be applied, is shown in U.S. Pat. No. 3,414,292 to S. Oldberg et al., assigned to the Assignee of the present invention.
In such known systems, the energized electro-explosive device may inflate the confinement directly with explosion product gases generated thereby, or may inflate the confinement indirectly, as by unblocking a flow of pressurized gas from a reservoir into the confinement.
So called nonpassive restraints, such as conventional noninflatable seat belts, shoulder straps and the like, are to be placed in operative restraining position by the vehicle occupant well before the time of a collision, preferably before the vehicle is put in motion. In contrast, passive restraints of the kind above discussed, are not normally placed in confining condition by the vehicle occupant but rather must be reliably and automatically inflated to their restraint condition during a collision.
The vehicle battery is conveniently the primary electrical power source for energizing the electro-explosive device which activates the passive restraint. However, rapid deceleration of the vehicle and/or structural damage thereto during a collision, particularly in early stages of the collision, may disconnect the vehicle battery from the safety system or otherwise render it incapable of supplying current to operate the passive restraint. In recognition of this possibility, the present Applicant in his aforementioned application Ser. No. 332,440 additionally provides a redundant power supply (a capacitor normally maintained charged by the vehicle battery) capable of energizing the passive restraint should the vehicle battery be disabled. Such a redundant power supply can be made relatively compact and light in weight and can be positioned protectively within the vehicle so as to remain operable despite disabling of the primary electrical power source.
Electro-explosive devices used in such passive restraint systems may be similar to the type disclosed in the aforementioned Pat. No. 3,414,292 of Oldberg et al. Applicant has recognized that known electro-explosive devices may short circuit their electrical connections after functioning. Such shorts would disable the electrical power supply inhibiting or preventing its further effectiveness. Thus, a redundant supply of limited current supply capability may thus be drained, inhibiting its further functioning.
Applicant has further recognized that while in certain instances it would be desirable to allow sequential operation of several electro-explosive devices independently from a common power source, as in response to sequential increases in deceleration rate, shorting of the power source by firing of a one electro-explosive device may thus preclude firing remaining electro-explosive devices, thus denying the desired protection to occupants at one or more passive restraint locations in the vehicle. Similarly, shorting of one electro-explosive device, where a plurality of same are fired simultaneously, would prevent proper firing of the other remaining electro-explosive devices of the plurality of same where a common current limited power supply is used.
This problem is complicated by the fact that, to be acceptable, passive restraint systems are expected to operate with an extremely high level of reliability, but yet must be manufacturable and installable within reasonable cost limits. The problem is further complicated by the fact that the safety system must react quickly, and during the course of a collision, to properly inflate the inflatable restraints, the time available from collision initiation to full restraint inflation normally being in the range of 40 to 60 milliseconds for a 30 mile per hour collision with a stationary barrier, thus requiring rapid actuation of an initial electro-explosive device and, where several electro-explosive devices are to act sequentially, rapid sequencing thereof.
Accordingly, the objects of this invention include provision of:
1. A vehicle safety system particularly capable of operating passive passenger restraints in a staged manner and in which a shorting of one or more stages does not inhibit functioning of other stages.
2. A system, as aforesaid, in which each stage includes at least one electro-explosive device and in which functioning of related stages is independent of and cannot be inhibited by shorting of an electro-explosive device in one stage.
3. A system, as aforesaid, which provides for automatic disconnection of a shorted electro-explosive device from its power source and prevents draining of such power source thereby, so as to enable functioning of other stages fed by such power source.
4. A system, as aforesaid, capable of disconnecting the shorted electro-explosive device from its power supply within a few milliseconds after shorting occurs.
5. A system, as aforesaid, which enables reliable firing of several electro-explosive devices in sequence, despite shorting or impermissible partial shorting in one or more thereof upon firing, by a power supply capable of delivering only a limited electrical charge (i.e., capable of delivering only a limited current for a limited period of time).
6. A system, as aforesaid, capable of providing increased reliability in operation of multiple stage inflatable passenger restraint arrangements and wherein such increased reliability is achieved at low cost and despite shorting in electro-explosive restraint actuation devices upon functioning.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.